By Ricardo Cardoso Reis (Planetário do Porto & Instituto de Astrofísica e Ciências do Espaço)

If you think you’re about to read about little green men, then you’ll be greatly disappointed. Please remember that the acronym UFO means “Unidentified Flying Object”, not “Alien Flying Saucer” (which would be AFS anyway…).

And that’s exactly what people are seeing at night, especially during the summer – “constellations” of flying lights in the sky. So, if they fly and you don’t know what they are (at least if you don’t skip and read ahead) they are, by definition, Unidentified Flying Objects.

These flying lights are the cause of many emails and phone calls we have received at the Centro de Astrofísica da Universidade do Porto (CAUP), the host institution for the Instituto de Astrofísica e Ciências do Espaço (Institute of Astrophysics and Space Sciences - IA) and the Porto Planetarium, in Portugal. The requests for explanations started about 2-3 years ago, and are more often during the summer months.

Now, I’m a sceptic, but the first time I got, on the same day, 3 different calls basically describing the same thing, from people in 3 different cities spanning over 100 km, even I started wondering what these people were seeing:

“I saw about 20 stars, all in formation, forming a triangle of sorts, plus a single lonely star behind the rest, that seemed to follow all the others, almost like a tail”.

Each time there is a sighting, the descriptions are consistent, but over the years, the events describe (apparently) very different phenomena:

“They moved together, like a flock of birds” say some, while others think “they each moved independently”. Sometime people describe “stars flashing rapidly” while others that they were not flashing at all and “had always the same brightness”. Often, they are described as having “lots of different colours, like blue, green and red”, other times as being “all white, all with the same brightness”.

It took a little digging to find the likely cause, but it turns out these UFO’s are just the 21st century version of what people in Porto are used to seeing every year, during St. Johns night.

These new UFO’s are, quite simply, LED Balloons!                                                                           

ricardo image

An LED light, with a small button cell powering it (like in the attached image), all inside a balloon filled with helium.

If you release a few dozens of these in an outdoors event, such as a wedding or a music festival, you can have multiple UFO sightings, spanning hundreds of kilometres.

As for the differences in the sightings, they are due to the diversity in the type of LED lights being used, which can have different colours, or be all the same colour, and can be set to blink, or not at all. The final variation is caused by the balloons themselves, which can be released all tied together, or separately.

Because balloon releases are most likely to occur in good weather, they are done essentially during the summer months (we tried doing a release here in Porto, at the end of September, during Researchers Night in Europe 2013, and it was a complete failure).

So, if you see lights moving in the sky (especially) during the summer, odds are you are not about to be abducted by aliens.



Ricardo Cardoso Reis works as science outreach officer at Instituto de Astrofísica e Ciências do Espaço (IA) and as planetarium producer/presenter at Planetário do Porto – Centro Ciência Viva, in Portugal. Between 2010 and 2012 he was solar activities coordinator for Global Astronomy Month. During the International Year of Astronomy 2009 (IYA2009) he was a member of the International task group and Portuguese co-coordinator for 100 Hours of Astronomy (and co-coordinator of “Sun Day” activity)  and Galilean Nights; and the International coordinator of Dawn of IYA2009, the first global event of IYA2009